Some benefits of dichotomization in psychiatric and criminological research

Abstract

Background: The product‐moment correlation r is widely used in criminology and psychiatry to measure strength of association. However, most criminological and psychiatric variables contravene its underlying assumptions. Aim: To compare statistical measures of association based on dichotomous variables with the use of r. Method: Explanatory variables for delinquency are investigated in the Pittsburgh Youth Study using a sample of 506 boys aged 13–14. Results: Dichotomization does not necessarily cause a decrease in measured strength of associations. Conclusions about the most important explanatory variables for delinquency were not greatly affected by using dichotomous as opposed to continuous variables, by different dichotomization splits, or by using logistic versus OLS multiple regression. Non‐linear relationships, interaction effects and multiple risk factor individuals were easily studied using dichotomous data. Conclusions: Dichotomization produces meaningful findings that are easily understandable to a wide audience. Measures of association for dichotomous variables, such as the odds ratio, have many advantages and are often more realistic and meaningful measures of strength of relationship than the product‐moment correlation r. Copyright © 2000 Whurr Publishers Ltd.